Diffusion pump



Dec. 23, 1958 L. FRANcl-:scHlNl 2,855,560

DIFFUSION PUMP Filed April 5, 1955 Imm i. Sgt@ 2,865,560 DIFFUSION PUMP Lorenzo Franceschini, Florence, Italy, assignor to Oliicine Galileo Societa per Azioni, Florence, Italy, a corporation of Italy Application April 5, 1955, Serial No. 499,472

Claims priority, application Italy April 10, 1954 8 Claims. (Cl. 230-101) posed of two combined elements, one of which forms the stage wherein there is the maximum volumetric capacity at the smallest pressure, and which will be referred to as the first stage, while the other element includes the other two stages forming a so-called booster unit.

The above mentioned features of small size combined-V with maximum eliiciency which are obtainable in this novel pump are essentially attributable to the arrangement of the device designed for the ejection of oil vapours and the devices designed for the condensing of said vapours, to provide greater efficiency and havingl im?, proved their operational distribution. Therefore -the liow.v of the oil vapours is divided in the rst stage of this pump in a plurality of jets, for which there is provided a large.

arent O 2,865,569 lsatented Dec. 23, 1953 Referring to the drawing, the molecules of airfrom a chamber (not shown) which is being evacuated` enter the top of the pump moving downwardly in the direction of the arrows designated a. In entering the pump, the

molecules enter a chamber wherein there is disposed a.

battery of tive nozzles or ejectors 2 and a central ejector 3. The ejectors 2 are connected to a central conduit or vertical pipe 4. Oil vapors are produced in a chamber 5 which is heated by a heater 6a disposed below the.

' bottom closure plate 6 of thechamber 5 and the heated surface exchange co-ndensing system. This pluralityv of"v y jets, which is equivalent to a plurality of pumps operati ling in parallel within the same stage, has the essential purpose of remarkably reducing the height of the chante. ber of the first stage relative to the height which saidl chamber would otherwise have for a single jet having vthe total capacity of the group of jets; in addition, the same plurality of jets is well suited to improve the distribution and increase, at the tame time, the effective heat exchange surface of the condensing devices, and the dynamic action of the oil vapour on the gas molecules is made more active, owing to a higher density of said vapour, and is better directed and also the condensation of the oil from.

its vapours is more complete, owing to this improvement. ln addition there is provided a thermal barrier between the first stage'and the two linal stages and while this barrier makes it possible to establish and maintain the lowest possible temperature at the transverse wall portion of cording to the invention, provision is made for separateheating and individual 'temperature regulation of'each of the three stages in order to provide improved cov-y ordination of operation.

The invention will now be described with referenc to the accompanying drawing.

Inthe drawing', the single ligure is a perspective viewI of a three stage diffusion pump embodying the invention,

the pump being partly broken away and shown insecti'on toillustrate details of construction. f

oil vapors are conveyed into the interior of said conduit 4, while the central ejector 3 is annular and is directly.

located around said conduit 4 with its own axis coinciding with the axis of said conduit. In the embodiment of the drawing, the ejectors 2 are illustratively shown as being tive in number but in practice the number of ejectors may vary in accordance with the capacity of the pump. These ejectors 2 are however arranged with au axial symmetry around the central conduit .4 and at an appropriate distance therefrom; the jets arriving from said ejectors, have their axes parallel to the axis of said conduit 4; said, jets are oriented towards the `bottom of the chamber (against the transverse plate 8 of a thermal barrier, later to be described) or however towards the so-called booster unit with an angular opening appropriately proportioned and defined by means of suitable.` detiectors 7. The condensation of the oil vapours occurs. on the inner surface of the wall 9 of the chamber and'v said wall is cooled Iby an appropriate liquid circulating' from an inlet hose fitting 1i) to an outletiitting 11, the coolant being confined in the hollow lspace 12 formed between said wall 9 and the outer casing 13 of the pump. Further condensation occurs along the walls of the partition members or bafes 14 formed by plates, vertically and radially extending among said jets always in such a way as to be symmetrical relative to the latter. The partitions,. formed of thermally conductivek material, located among the jets, are cooled at their lower edges by a conduit 15, wherein thev refrigerant liquid is' cir- 1S. A portion of the thus condensed oil vapor iiows along the inner surface of the wall 9 of the chamber,v

while -a portion thereof flows downwardly along the 'par` titions 14 and is collected by the annular gutter 16 from. which it is discharged downwardly through the drains 17.

The residue of air, vhaving a high volume and low pressure, downwardly urged by'the dynamic eiiect of the oil vapor jets, then enters the second stagetbelonging to the booster unit); in this second stage, according to the invention, the oil vapours heated in the chamber 18, coaxial with the chamber 5l of the first stage, by the heating elements 19, emerge through the annular ejector'Ztl defined by a space between the lowermost plate 20 of the thermal barrier. The thermal barrier is formed by a series of four vertically spacedplates 8, 29, 30 and 20. The downwardly deected jet of emerging vapor comes in contact with the cooled inner surface of the wall 9 and is progressively condensed during its downward movement toward the bottom of the pump. The

residue of air, reduced toa medium volume with anv v increase of pressure, passes into the zone of the third ing chamber 22 is present. This jet is directed toward the annular condenser 24 provided with corrugations 3 which enlarge its heat exchange surface. The condenser 24 is strongly coo-led by liquid which iiows through the conduits 2S and 26. The residue of air, which nally has attained the smallest volume with the high'estpressure, passes from theY chamber iof this condenser through the outlet iittings 27 in the direction of. the` arrow` designated b and into the preliminary air pturip,- notl indicated in the drawing.

t Each of the downwardlyopeiiingconical deliectors 7 each other through small apertures 31 formed at the bases of the partitions which define the chambers. These apertures are located adjacent to the heated base platev 6 and permit the flow of condensed oil from a collecting trough 32 through apertures 33 therein to the base plate 6 for redistribution over the entire area of base plate 6 so that the oil is again vaporized and reused.

If desired, the upper element S of the thermal barrier 849-30120 may also be cooled like Vthe radially extending bailleu members 14 and the cylindrical wall 9. Such cooling will further tend to reduce possible re-evaporation of oil vapor droplets formed in the condenser 1.

In operation, the gas molecules entering the condenser 1 are drawn. downwardly by the acti-on of the oil vapor jets issuing from the` nozzles 2; the jets being appropriately confined and directed by the conical deectors 7. The oil vapor;i which entrains the gas molecules, is `condensed by contact with vthe radial bales 14 while vits upward escape from the pump is prevented by condensationv in the condenser 1. The thermal barrier 849-30120 prevents re-evap'oration of oil droplets formed in the first stage of the pump;

After leaving the first stage, ythe gas molecules are again entrained and urged toward the pump outlet 27 by further successive .jets of oil vapor, annular in form.

Iissuing from the annular apertures 2li and 21 disposed inthe lower portion ofV the pump.

While I have shown what I believe to be the best embodiment of my invention, it will be apparent to those skilled in the art 'that various modifications may be rnade therein without departing from the spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A vacuum ditius'ion pump comprising a lateral Wall defining a chamber, said chamber being provided withv an upper inlet and a lower outlet, means included in said wall for cooling said wall, transversely extending thermal barrier means dividing said chamber int-o an upper section and a lower section, said barrier -means being spaced from said wall -to define a first annular passageway therewith, closure means for vsaidloiiver section disposed at the bottom `ol: said chamber, means for supplying heat to said closure means, a pipe extending from saidclosure means in said lower section through 'said transverse barrier'mean's into said upper section, a plurality Iof downwardly directed nozzles disposed at regularly spaced locations in said upper section 'and communicating with said pipe, `and a first annular partition wall said lower section extending from said 'closure means 'to a location spaced from said barrier' means toY define a second annular passageway therewith, Asaid first partition wall being coaxial with said pipe, whereby upon corinecting said inlet to ra vessel to be. evfacuated and said outlet to a pump, heating of a yliquid placed on lsaid closuremeans v-crai'rses said liquid to 'vaporize, a portion of thext fhapors rising through said pipe and A,being `c lireazteil downwardly in said upper section in a series of parallel generated between said streams through said nozzles, said vapors entraining the gas to be removed from said vessel and being cooled and condensed by said lateral wall, the gas passing downwardly through said first annular passageway to be carried along to said outlet by further vapor generated between said pipe and said first partition wall, the further vapor passing first upwardly between said pipe and first partition` wall and then being deflected through said second afi''uler' passageway by said barrier means to pass downwardly between said first partition wall and said lateral wall.

2. A pump as' defined in claim l, further comprising a plurality of bafes in said upper section extending radially from said pipe toward said outer wall and each extending between two adjacent one of said nozzles.

3. A pump as dened in claim 2 further comprising means including a circulation duct disposed in thermally conductive relationship with respect to said baffles, said duct extending exteriorly of said chamber and beingr adapted to receive and circulate a coolant therein for cooling Said baiiies, and means disposed below said baiiies for receiving condensate formed on said bailies.

4. A pump as defined in cla'im l, further comprising a second annular partition wall disposed between said first partition wall and said lateral wall, said second wall extending vfrom said closure means toward said first partitiori wall to define a third annular passageway therewith, said rst partition wall being provided with a downturned lip above said third annular passageway to detlect downwardly vapor generated between said lirst and second partition walls.

5. A' vacuum diffusion pump comprising an outer 'wall defining a chamber, said chamber being provided withxan upper inlet and a lower outlet, means included in vsaid outerwall for cooling 4said outer wall, transversely extending Athermal barrier means dividing said chamberinto an 'upper section 'and a lower section, the periphery of said barrier means being spaced from said wall to define a first annular passageway therewith, a

closure for said lower section disposed at the bottom oflsaid chamber, means for supplying heat to said closure, a pipe extending from said closure in said lower section through said barrier means into said upper section, a plurality of baies in Said upper section extending radially from said pipe toward said outer wall, a plurality of downwardly directed nozzles communicating with said pipe and each disposed in said upper section between two adjacent ones of said baflles, and a first annular partition wall in said lower section extending from said closure to a location spaced from said barrier means to denne a second annular passageway therewith, said first partition wall being coaxial with said pipe, whereby upon connecting said inlet to a vessel to be evacuated and said outlet to a pump, heating of a liquid placed on said closure causes said liquid to vaporize, a

portion of thevapors rising through saidpipe and beingv directed downwardly in said upper section in 'a series ofhparallel streams through said nozzles, said vapors entraining the gas to be removed l'from said vessel and being cooled and condensed by said outer wall, the gas passing downwardly through said first annular passageway to be carried along to said outlet by further vapor y pipe and said first partition wall, the further vapor passing iii-st upwardly between said pipe and first partition wall and then Ibeing deflected through said second annular passageway by said barrier means to pass downwardly between said irst partition wall and said outer wall.

6. A pump as defined in claim 5, vfurther comprising a condenser within said upper section between said inlet and said nozzles, and a hood disposed above each of said nozzles, 4whereby any vapor condensed by said condenser `isjprevented by said hood from falling 'onto a nozzle which has been heated by said Ip'ortion of'fthe vapors rising through said pipe.

7. A vacuum diffusionpump comprising a cylindrical outer wall defining a chamber and provided with an upper inlet and a lower outlet, thermally insulative transverse separation means Vdividing said chamber into an upper section and a lower section, said separation means being spaced from said wall to define a iirst annular passageway therewith, means included in said outer Wall for cooling said sections, a closure for said lower section disposed at the bottom of said chamber, heating means disposed in thermally conductive relationship with respect to said closure for supplying heat to said closure, a pipe extending from said closure in said lower section through said transverse separation means into said upper section, a plurality of batlies in said upper section extending radially from said pipe toward said outer wall,

' means for cooling said bales, means including a circulation duct disposed in thermally conductive relationship with respect to said bales, said duct extending exteriorly of said chamber and being adapted to receive and circulate a coolant therein disposed beneath said bafes for receiving condensate formed on said baffles, a plurality of downwardly directed nozzles communicating with said pipe and each disposed in said upper sec tion between two of said baffles, rst and second annular partition walls in said lower section extending upwardly 25 from said closure coaxially with said pipe, said rst partition wall dening a second annular passageway with said transverse separation means and being provided with a downturned lip, said second partition wall dening with said downturned lip a downwardly directed third annular passageway, whereby upon connecting said inlet to a vessel to be evacuated and said outlet to a pump, heating of a liquid placed on said closure causes said liquid to vaporize, a portion of the vapors rising through said pipe and being directed downwardly in said upper section in a series of parallel streams through said nozzles, said vapors entraining the gas to be removed from said Vessel and being cooled and condensed by said outer wall, the gas passing downwardly through said iirst annular passageway to be carried along to said outlet by further downwardly directed vapor generated between said pipe and said rst partition wall and between said partition walls.

8. A pump as dened in claim 7, wherein said means for supplying heat to said closure is subdivided into separately heated portions for independently heating liquid furnishing vapor to said pipe, between said pipe and said first partition wall, and between said first and second partition walls.

References Cited in the le of this patent UNITED STATES PATENTS 2,112,037 Malter Mar. 22, 1938 2,291,054 Nelson July 28, 1942 2,508,765 Morand May 23, 1950 

